Abdominal Aortic Aneurysm

See Also

Abdominal Pain in Older Adults

Definitions

Abdominal Aortic Aneurysm
1. Abdominal aorta diameter 3.0 cm or greater
Abdominal Aortic Ectasia
1. Abdominal aorta diameter 2.5 to 2.9 cm

Epidemiology

Ruptured AAA results in 11,000 deaths per year
1. Responsible for 4-5% of sudden deaths in the United States
Age Distribution
1. Age under 50 years old
  1. Uncommon
2. Age over 60 years
  1. Incidence 5-7% of over 60 years old
  2. Accounts for 75% of aneurysms
3. Age 65 to 74 years old
  1. Tenth leading cause of death
4. Ages 74-84 years old
  1. Men: 12.5% Incidence of AAA
  2. Women: 5.2% Incidence of AAA
Male:Female Ratio
1. Age: 60-64 year old: 11:1
2. Age: 85-90 year old: 3:1
Ethnicity
1. Black and hispanic patients are at lower risk of AAA

Pathophysiology

Elastin and collagen degradation in aorta wall
Provoked by environmental stressors
1. Inflammation (esp. Tobacco Abuse)
2. Possible association with Chlamydia pneumoniae
3. Increased wall tension (e.g. Hypertension, PVD)

Risk Factors
AAA Development

Similar to other Cardiovascular Risk Factors
Tobacco Abuse (90% of patients have used Tobacco)
First degree relative has up to a 19% risk of AAA
Coronary Artery Disease (including prior Myocardial Infarction)
Peripheral Arterial Disease
Hypertension
Age over 65 years old
Male gender

Risk Factors
AAA Rupture

Female gender
Tobacco Abuse
Obstructive Lung Disease (FEV1 decreased)
Hypertension

Causes

Associated with Atherosclerosis in only 25% of patients
Aortic Dissection
Mycotic Infection
Cystic Medial Necrosis
Ehlers-Danlos Syndrome

Presentation

Asymptomatic in 75% of AAA
Abrupt onset severe pain unrelieved by position change
1. Classic: Back pain or Abdominal Pain, pulsatile mass and Hypotension
2. Suggestive of aneurysm enlargement or rupture
3. Classic triad only present in 25-50% of cases
Cryptic presentations are common
1. Misdiagnosis as Diverticulitis, GI Bleed, Musculoskeletal cause is common (60% initial misdiagnosis rate)
2. May present as referred pain to a wide range of regions (to chest, back and Scrotum)
3. Microscopic Hematuria (and rarely Gross Hematuria) may lead to misdiagnosis of Renal Colic
Aortic Rupture (20% present ruptured)
1. Free Intraperitoneal Rupture (Catastrophic)
  1. Acute abdominal or back pain
  2. Flank Ecchymosis
  3. Cardiovascular Collapse (Hypotension)
  4. Sudden Death
2. Sentinal Bleed (small posterolateral wall tear)
  1. Acute pain (constant)
  2. Syncope
  3. Pulsatile abdominal mass
  4. Hemodynamically stable with Tachycardia
  5. Needs Emergent Intervention before full rupture

Symptoms

Pain in Abdomen, Flank or Back
Early satiety
Nausea and Vomiting

Signs
Pulsatile abdominal mass

Technique
1. Mass occurs left of midline at level of Umbilicus
2. Position patient supine, knees flexed, while exhaling
3. May be associated with abdominal bruit
Efficacy of palpation for pulsatile mass >3 cm
Larger AAA has higher likelihood of palpation
1. AAA 3-4 cm palpable in 29% of cases
2. AAA 5 cm palpable in 76% of cases
3. Lederle (1999) JAMA 281:77-82 [PubMed]

Signs
Peripheral pulses

Check pulse
1. Femoral artery
2. Popliteal artery
Interpretation
1. Bounding Pulse suggests possible AAA
2. Peripheral artery aneurysmal swelling
  1. Femoral aneurysm predicts AAA in 85% of cases
  2. Popliteal aneurysm predicts AAA in 62% of cases

Signs
Miscellaneous

Cullen's Sign
1. Periumbilical Bruising
Grey Turner's Sign
1. Flank Bruising (retroperitoneal hematoma)

Differential Diagnosis

Diagnosis

AAA is most commonly identified as an Incidental Imaging Finding
Normal abdominal aorta diameter
1. Male: 17-21 mm (infrarenal)
2. Female: 15-19 mm (infrarenal)
Abnormal Localized aortic dilatation
1. Aortic diameter exceeds 1.5 times normal size
2. Aortic diameter exceeds 30 mm

Imaging
General

See Ultrasound in Abdominal Aortic Aneurysm
See CT in Abdominal Aortic Aneurysm
Incidental Findings on Abdominal XRay (low Specificity)
1. Calcified AAA wall visible in only 67-75%
2. Soft tissue mass
3. Loss of psoas shadow
4. Loss of renal outline

Imaging
Screening for Abdominal Aortic Aneurysm

Indications for one-time routine screening
1. USPTF Guidelines (2014)
  1. General screening above age 75 years is not typically recommended due to likelihood of comorbidity
  2. Men 65 to 75 years old
    1. History of Tobacco Abuse (>100 Cigarettes lifetime, Level B recommendation)
    2. Other AAA Risk Factor (see risk factors above, Level C recommendation)
  3. Women 65 to 75 years old
    1. History of Tobacco Abuse (inconclusive, consider screening)
2. Society for Vascular Medicine Guidelines
  1. Men age 60 to 85 years
  2. Women age 60 to 85 years with Cardiac Risk Factors
  3. Men and Women age >50 years and history of AAA in first degree relative
First choice imaging study
1. See Ultrasound in Abdominal Aortic Aneurysm
Alternative for Obesity or excess intestinal gas
1. Standard CT (see CT in Abdominal Aortic Aneurysm)

Imaging
Monitoring protocol for Abdominal Aortic Aneurysm

Ultrasound in Abdominal Aortic Aneurysm
1. Aorta diameter <3.0 cm
  1. No surveillance (although some consider rescreening if 2.5 to 2.9 cm)
2. Aorta diameter 3.0 to 3.9 cm
  1. Repeat Ultrasound of AAA every 2 to 3 years
  2. Typical rate of expansion: 1-4 mm/year
3. Aorta diameter 4.0 to 5.4 cm
  1. Repeat Ultrasound of AAA (or CT in Abdominal Aortic Aneurysm) every 6-12 months
  2. Consider Surgical Consultation for AAA 5.0 cm or greater (or faster rate of expansion)
  3. Typical rate of expansion: 3-5 mm/year
4. Aorta diameter >5.4 cm
  1. Surgical Consultation for elective AAA repair
  2. Typical rate of expansion: 7-8 mm/year (for AAA >6.0 cm)
CT in Abdominal Aortic Aneurysm
1. Indications
  1. Surgeon will order on referral
  2. See surgery indications below
  3. Ultrasound aorta >5.4 cm
  4. Change >0.5 cm in 6 months or >1 cm in 1 year
2. Interpretation
  1. Repeat Ultrasound q3 months if aorta <5.5 cm
  2. Vascular surgery consult for indications below
  3. Admit patients with aorta >8 cm on CT Abdomen

Imaging
Preoperative evaluation

First Choice
1. CT Angiogram
Alternative in specific circumstances
1. Abdominal Aortography
2. MRI with MRA in abdominal aortic aneurysm

Precautions

Delayed diagnosis of AAA related symptoms has a very high mortality
Have a low threshold for bedside Abdominal Aorta Ultrasound in age >50-60 years with Abdominal Pain or back pain

Management
Surgical Repair

Indications: Symptomatic Aneurysm
1. Symptoms: Abdominal, back or Groin Pain with AAA
  1. Concurrent Hypotension suggests ruptured AAA
2. Urgent surgical repair (high risk of rupture)
Indications: Asymptomatic Aneurysm
1. Aortic aneurysm diameter >5.4 cm
2. AAA diameter 4-5 cm and
  1. Enlarging 0.5 cm in 6 months or
  2. Enlarging 1 cm in 1 year
3. AAA diameter 7 cm with significant comorbidity
  1. Left Ventricular Dysfunction (CHF)
  2. Severe Chronic Obstructive Pulmonary Disease
  3. Noncorrectable symptomatic Coronary Artery Disease
Operative Risk
1. Myocardial Infarction (4.7% mortality)
2. Mortality
  1. Elective repair: 3-5% (similar risk )
  2. Symptomatic Aneurysm: 26%
  3. Ruptured Aneurysm: 35-40%
  4. Sullivan (1990) J Vasc Surg 11:799-803 [PubMed]
Operative techniques
1. Open AAA repair (traditional)
  1. Higher 30 day mortality (4-5%) than endovascular repair (1-2%)
    1. However, endovascular repair benefit is absent by 1-2 years following repair
    2. Greenhalgh (2010) N Engl J Med 362(20): 1863-71 [PubMed]
  2. Endovascular repair has a higher rate of later complications
    1. Graft complications
    2. Second procedures required
2. Endovascular AAA repair (Endograft)
  1. Optimal emergency stabilization procedure if infrarenal AAA (especially in elderly patients)
  2. Also consider if high risk with <2 years Life Expectancy
  3. Surveillance post procedure
    1. Requires CT at 1, 6 and 12 months after procedure
    2. Annual surveillance required after the first year
  4. Adverse events (10-15%)
    1. Lower 30 day mortality than open AAA repair
    2. Risk of blood leakage around endograft
    3. Also risk of stent graft or migration
    4. Similar 5 year mortality outcomes to open repair
  5. References
    1. (2005) Lancet 365:2179-86 [PubMed]
Preoperative risk reduction
1. See Preoperative Cardiovascular Evaluation
2. Perioperative Beta Blocker
  1. Significantly decreases mortality
  2. Used bisoprolol 5 mg daily >1 week pre-surgery
  3. Goal Heart Rate: 60 (keep systolic BP >100)
  4. Poldermans (1999) N Engl J Med 341:1789-94 [PubMed]
3. Tobacco Cessation
4. Statins for lipid lowering
5. COPD optimization
6. Renal Function optimization in Chronic Kidney Disease

Prognosis

Mortality from ruptured aneurysm: 90% (50% do not reach the hospital alive)
Elective AAA Repair: 61% five year survival
Risk of AAA rupture
1. AAA <5.5 cm: 0.6-3.2% annual risk of AAA rupture
2. AAA 5.5 - 6 cm: 9% annual risk of AAA rupture
3. AAA 6 - 6.9 cm: 10% annual risk of AAA rupture (40% lifetime risk of rupture)
4. AAA 7 cm: 33% annual risk of AAA rupture (50% lifetime risk of rupture)
Course of small aortic aneurysms (<4 cm)
1. Increase median of 2 mm per year (up to 8 mm/year)
2. Biancari (2002) Am J Surg 183:53-5 [PubMed]
Comorbid cardiopulmonary disease is common in AAA

Prevention

Slowing progression of AAA
1. Tobacco Cessation
  1. Tobacco increases the incremental AAA growth rate by 0.4 mm per year
  2. Sweeting (2012) Br J Surg 99(5): 655-65 [PubMed]
2. No strong evidence for specific antihypertensives or lipid lowering agents prior to repair
Patient Education
1. Indication for immediate evaluation in known AAA
2. Pain in low back, groin, legs or buttocks

References

Weinstock in Herbert (2018) EM:Rap 18(6): 2-3
Brewster (2003) J Vasc Surg 37:1106-17 [PubMed]
Keisler (2015) Am Fam Physician 91(8): 538-43 [PubMed]
Lederle (2003) Ann Intern Med 139:516-23 [PubMed]
Newell (1997) Am Fam Physician 56(4):1103-8 [PubMed]
Santilli (1997) Am Fam Physician 56(4):1081-90 [PubMed]
Upchurch (2006) Am Fam Physician 73(7):1198-206 [PubMed]